Ferroelectric CsGeI₃ Single Crystals with a Perovskite Structure Grown from Aqueous Solution

All-inorganic perovskite halide semiconductors have been noticed for applications in photovoltaics, light-emitting diodes, lasers, and photodetectors, thanks to their exceptional optoelectronic characteristics. As a typical example, CsGeI₃ was previously investigated in the forms of quantum dots and thin films. Here, we developed a technique based on aqueous solution to synthesize millimeter-level-sized CsGeI₃ single crystals. The ferroelectric and photoelectric functionalities of the as-grown crystals were examined and compared with the prediction from density functional theory calculation. These findings not only provide a new route to make germanium-based perovskite single crystals but also introduce possible prospects for ferroelectric photovoltaics.